Physical quantity sensor having multiple through holes

ABSTRACT

A semiconductor physical quantity sensor includes: a substrate; a semiconductor layer supported on the substrate; a trench disposed in the semiconductor layer; and a movable portion disposed in the semiconductor layer and separated from the substrate by the trench. The movable portion includes a plurality of through-holes, each of which penetrates the semiconductor layer in a thickness direction. The movable portion is capable of displacing on the basis of a physical quantity applied to the movable portion so that the physical quantity is detected by a displacement of the movable portion. The movable portion has a junction disposed among the through-holes. The junction has a trifurcate shape.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on Japanese Patent Applications No.2004-118887 filed on Apr. 14, 2004, and No. 2004-133657 filed on Apr.28, 2004, the disclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a physical quantity sensor havingmultiple through holes.

BACKGROUND OF THE INVENTION

A dynamic-quantity semiconductor sensor (i.e., a physical quantitysensor) of prior art comprises a base plate and a semiconductor layer.The semiconductor layer is supported on the base plate. Through trenchesare made in the semiconductor layer by etching. The semiconductor layerhas a movable part, which is defined by the trenches and released fromthe base plate. The sensor is, for example, disclosed in Japanese PatentApplication Publication No. 2001-91265.

The dynamic-quantity semiconductor sensor detects the applied dynamicquantity, i.e., the physical quantity, based on the displacement of themovable part when dynamic quantity such as angular velocity oracceleration is applied to the sensor.

For example, Japanese Patent Application Publication No. 2001-133268discloses an angular-velocity sensor which is made of an SOI(Silicon-On-Insulator) substrate consisting of two silicon plates and anoxide film, the oxide film sandwiched between the silicon plates.

The above sensors of prior art are so-called dynamic-quantitysemiconductor sensors of the surface-processing type. They are made asfollows. One of the two silicon plates of an SOI substrate is asupporting base plate and the other is a semiconductor layer. Trenchetching is made from the top-surface side of the semiconductor layer toform the pattern of a structure including a movable part. Then, themovable part is released by removing the lower part of the semiconductorlayer by side etching or removing the oxide film by sacrifice-layeretching.

Besides, a plurality of through holes is made in the movable part toraise the efficiency of etching and reduce the weight of the movablepart. This is disclosed in, for example, Japanese Patent ApplicationPublication No. 2001-99861.

The above dynamic-quantity semiconductor sensors of prior art have thefollowing problems. In the step of releasing the movable part by etchingfrom the through holes, the finished shapes of various parts of themovable part become considerably uneven, the characteristics of movableparts vary, and the strength of the movable part deteriorates.

SUMMARY OF THE INVENTION

In view of the above-described problem, it is an object of the presentinvention to provide a physical quantity sensor with multiple throughholes having small manufacturing error.

A semiconductor physical quantity sensor includes: a substrate; asemiconductor layer supported on the substrate; a trench disposed in thesemiconductor layer; and a movable portion disposed in the semiconductorlayer and separated from the substrate by the trench. The movableportion includes a plurality of through-holes, each of which penetratesthe semiconductor layer in a thickness direction. The movable portion iscapable of displacing on the basis of a physical quantity applied to themovable portion so that the physical quantity is detected by adisplacement of the movable portion. The movable portion has a junctiondisposed among the through-holes. The junction has a trifurcate shape.

In the above sensor, a distance between the periphery of the junctionand the center of the junction becomes smaller comparatively. Therefore,when the movable portion is separated in a release etching process, theetching time, i.e., the process time becomes shorter so that themanufacturing deviation of the movable portion is reduced. Accordingly,the sensor has small manufacturing error.

Preferably, each through-hole has a rectangular shape, and thethrough-holes are arranged to be houndstooth check structure.Preferably, each through-hole has a hexagonal shape, and thethrough-holes are arranged to be honeycomb structure. Preferably, themovable portion provides a through-hole frame having a plurality ofjunctions. The frame is made of a plurality of rods having a width in ahorizontal direction perpendicular to the thickness direction. The widthof the rod is uniformed, and the junctions are provided by anintersection of the rods.

Further, a semiconductor physical quantity sensor includes: a substrate;a semiconductor layer supported on the substrate; a trench disposed inthe semiconductor layer; and a movable portion disposed in thesemiconductor layer and separated from the substrate by the trench. Themovable portion includes a plurality of through-holes, each of whichpenetrates the semiconductor layer in a thickness direction. The movableportion is capable of displacing on the basis of a physical quantityapplied to the movable portion so that the physical quantity is detectedby a displacement of the movable portion. The trench adjacent to themovable portion has a width capable of performing a maximum etching rateof the semiconductor layer adjacent to the trench.

In the above sensor, the movable portion is separated from the substratewith using the trench in the movable portion and the trench disposedouter periphery of the movable portion in a release etching process whenthe sensor is manufactured. At this time, the trench adjacent to themovable portion has a width capable of performing a maximum etching rateof the semiconductor layer adjacent to the trench. Therefore, themovable portion can be separated from the substrate with a short etchingtime. Thus, the movable portion is separated accurately from thesubstrate in the manufacturing process. Accordingly, the sensor hassmall manufacturing error.

Preferably, the trench having the width capable of performing themaximum etching rate is disposed in the movable portion. Preferably, thetrench further includes a second width and a third width. The trenchhaving the second width or the third width is disposed outer peripheryof the movable portion. The second width is wider than the third width.The trench having the width capable of performing the maximum etchingrate in the movable portion is disposed neighboring to the trench havingthe second width. More preferably, the trench in the movable portiondisposed neighboring to the trench having the third width is capable ofperforming a later etching rate later than that of the trench in themovable portion disposed neighboring to the trench having the secondwidth.

Preferably, the etching rate and the width of the trench have arelationship in such a manner that the maximum etching rate is obtainedin a case where the width of the trench is around 7 μm. More preferably,the etching rate and the width of the trench include furtherrelationship in such a manner that the etching rate substantiallybecomes zero in a case where the width of the trench is equal to orlarger than 10 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

FIG. 1 is a plan view showing a semiconductor acceleration sensoraccording to a first embodiment of the present invention;

FIG. 2 is a cross sectional view showing the sensor taken along lineII—II in FIG. 1;

FIG. 3 is a partially enlarged plan view showing a part III of thesensor shown in FIG. 1;

FIGS. 4A to 4C are cross sectional views explaining a method formanufacturing the sensor according to the first embodiment;

FIG. 5 is a circuit diagram showing a detection circuit of the sensoraccording to the first embodiment;

FIG. 6 is a partially enlarged plan view showing a main part of asemiconductor acceleration sensor according to a second embodiment ofthe present invention;

FIG. 7 is a partially enlarged plan view showing a main part of asemiconductor acceleration sensor according to a modification of thesecond embodiment;

FIG. 8 is a partially enlarged plan view showing a main part of asemiconductor acceleration sensor according to another modification ofthe second embodiment;

FIG. 9 is a plan view showing a semiconductor acceleration sensoraccording to a comparison of the first embodiment;

FIG. 10 is a cross sectional view showing the sensor taken along lineX—X in FIG. 9;

FIG. 11 is a partially enlarged plan view showing a part XI of thesensor shown in FIG. 9;

FIG. 12 is a plan view showing a semiconductor angular velocity sensoraccording to a third embodiment of the present invention;

FIG. 13 is a cross sectional view showing the sensor taken along lineXIII—XIII in FIG. 12;

FIG. 14 is a partially enlarged plan view showing a part XIV of thesensor shown in FIG. 12;

FIGS. 15A to 15C are cross sectional views explaining a method formanufacturing the sensor according to the third embodiment;

FIG. 16 is a graph showing a relationship between a trench width and anetching rate, according to the third embodiment; and

FIG. 17 is a partially enlarged plan view showing a main part of asemiconductor angular velocity sensor according to a comparison of thethird embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(First Embodiment)

The inventors have preliminarily studied about a physical quantitysensor. FIG. 9 is a schematic plan view of the sensor. FIG. 10 is aschematic sectional view along the line X—X of FIG. 9. FIG. 11 is anenlarged view of the part XI of FIG. 9.

Such acceleration sensors are made by processing a semiconductorsubstrate 10 with a well-known micro-machine.

As shown in FIG. 10, the semiconductor substrate 10 of the experimentalacceleration sensor is a rectangular SOI substrate 10 comprising a firstsilicon plate 11 as a supporting base plate, a second silicon plate 12as a semiconductor layer, and an oxide film 13 as an insulating layertherebetween.

The second silicon plate 12 is trench-etched to form trenches 14,through holes 26, a movable part 20, and fixed electrodes 31 and 41. Themovable part 20 has beam parts 22 and movable electrodes 24. The movableelectrodes 24 are formed as one body with beam parts 22. The fixedelectrodes 31 and 41 are arranged opposite to the movable electrodes 24.

The trench etching is made from the top-surface side of the secondsilicon plate 12 to form the pattern of a structure including themovable part 20. Then, the lower part of the second silicon plate 12 isremoved by side etching to release the movable part 20. Because the sideetching is made through the through holes 26, the etching is efficient.

Each beam part 22 is in the shape of beams extending in the directionperpendicular to the “X” direction shown in FIG. 9 and has a springfunction to move in “X” direction in accordance with the application ofdynamic quantity. The movable electrodes 24 are formed as one body withthe beam parts 22 and disposed at intervals along the “X” direction andmove in “X” direction together with the beam parts 22.

The fixed electrodes 31 and 41 are fixed onto and supported on the firstsilicon plate 11. The fixed electrodes 31 and 41 and the movableelectrodes 24 are arranged alternately, and the side surfaces of fixedelectrodes 31 and 41 and those of the movable electrodes 24 face eachother.

When acceleration is applied to the acceleration sensor in the “X”direction, the capacity “CS1” between the left fixed electrodes 31 andthe movable electrodes 24 and the capacity “CS2” between the right fixedelectrodes 41 and the movable electrodes 24 change.

A signal based on the difference between the changed capacities(CS1−CS2) is outputted, processed by a circuit, etc. (not shown), andfinally outputted. In this way, acceleration is detected.

As shown in FIGS. 9 to 11, according to such the acceleration sensor,the through holes 26 of the movable part 20 are rectangular.

There are junctions 28 of four straight parts of the hole frame 27around the through holes 26.

As shown in FIG. 11, the distance “L3” from the perimeter to the center“K” of each junction 28 is about 1.4 times (√{square root over (2)}times) the distance “L2” from the periphery of each through hole 26 tothe center of any straight frame part around said through hole 26.Specifically, the distance L3 is defined between the center K and acorner of the junction 28, and the distance L2 is defined between acenter line and a side of the junction 28.

Even with the through holes 26 of the shape and arrangement shown inFIGS. 9 to 11, the movable part 20 can be released by etching. However,the etching time necessary to release each part of distance “L3” is 1.4times the etching time necessary to release each part of distance “L2.”Accordingly, the finished shapes of various parts of the movable part 20vary considerably.

Besides, when we try to release the parts of distance “L3” completely,the parts of distance “L2” are overetched, and the straight parts of thehole frame 27 between the through holes 26 rendered too narrow and thin.

In view of the above problem, a physical quantity sensor according to afirst embodiment of the present invention is provided. Specifically, inthis embodiment, the present invention is applied to an accelerationsemiconductor sensor of a differential capacity type (capacity-typeacceleration sensor) as a semiconductor dynamic-quantity sensor. Thisacceleration sensor can be applied to acceleration sensors forautomobiles and gyro-sensors for controlling the workings of air bags,ABS, VSC, etc.

FIG. 1 is a schematic plan view of an acceleration sensor 100 inaccordance with the present embodiment. FIG. 2 is a schematic sectionalview along the line II—II of FIG. 1. FIG. 3 is an enlarged view of thepart “III” of FIG. 1.

This acceleration sensor 100 is formed by processing a semiconductorsubstrate 10 with a micro-machine.

As shown in FIG. 2, the semiconductor substrate 10 is a rectangular SOIsubstrate 10 comprising a first silicon plate 11 as a supporting baseplate, a second silicon plate 12 as a semiconductor layer, and an oxidefilm 13 as an insulating layer therebetween.

Trenches 14 are formed in the second silicon plate 12 to form a beamstructure which comprises a movable part 20 and fixed parts 30 and 40and is in the shape of a comb's teeth.

As shown by a broken-line in FIG. 1, a rectangle part 15 of the beamstructure 20-40 of the second silicon plate 12 is made thin so thatthere exists a gap between the thin part of the second silicon plate 12and the oxide film 13. The part will hereinafter be called “thin part15” of the second silicon plate 12.

The movable part 20 comprises a long, narrow rectangular weight part 21which is connected to anchor parts 23 a and 23 b through the medium of aspring part as a beam part 22.

The anchor parts 23 a and 23 b are fixed onto the oxide film 13. Thus,they are supported on the first silicon plate 11 through the medium ofoxide film 13. Accordingly, the weight part 21 and the spring part 22are separated from the oxide film 13.

As shown in FIG. 1, the spring part 22 comprises two parallel beams,which are connected at both of their ends to have the shape ofrectangular frame, and has a spring function to allow the weight part 21to move in the direction perpendicular to the beams.

To be specific, the spring part 22 allows the weight part 21 to move inthe “X” direction when the acceleration sensor 100 is exposed toacceleration containing a component in an “X” direction parallel to thesemiconductor substrate 10 as shown in FIG. 1. When the accelerationceases, the spring part 22 allows the weight part 21 to revert to itsoriginal static position.

Thus, the weight part 21, which is connected to the semiconductorsubstrate 10 through the medium of spring part 22, can move over thefirst silicon plate 11, in the “X” direction when the accelerationsensor 100 is exposed to acceleration containing a component in an “X”direction parallel to the semiconductor substrate 10.

As shown in FIG. 1, the movable part 20 has movable electrodes 24 as thethin part 15, which are a plurality of beams extending from both sidesof the movable part 20 outward like the teeth of a comb.

In other words, the movable electrodes 24 are arranged at intervalsalong the longitudinal direction of the weight part 21 (“X” direction)and extending outward like the teeth of a comb.

In FIG. 1, four movable electrodes 24 are formed on each side of theweight part 21. Each movable electrode 24 has a rectangular crosssection and is separated from the oxide film 13.

Thus, the movable electrodes 24 are formed as one body with the weightpart 21 and the spring part 22; accordingly, the movable electrodes 24can move in “X” direction parallel to the semiconductor substrate 10together with the weight part 21 and the spring part 22.

As shown in FIGS. 1 and 2, the fixed parts 30 and 40 are fixed to theoxide film 13 on the two opposite sides of the thin part 15 other thanthe two opposite sides where the anchor parts 23 a and 23 b exist. Thus,the fixed parts 30 and 40 are supported on the first silicon plate 11through the medium of the oxide film 13.

In FIG. 1, the fixed part 30 on the left side of the weight part 21comprises left fixed electrodes 31 and a wiring part 32 for the leftfixed electrodes 31 and the fixed part 40 on the right side of theweight part 21 comprises right fixed electrodes 41 and a wiring part 42for the right fixed electrodes 41.

As shown in FIG. 1, the left and right fixed electrodes 31 and 41 arewithin the thin part 15 and the fixed electrodes and the movableelectrodes are arranged alternately on both sides of the weight part 21.

As shown in FIG. 1, four pairs of fixed and movable electrodes areprovided on each side of the weight part 21, and the fixed electrode 31is disposed above the movable one in each pair on the left side of theweight part 21 and the movable electrode 41 is disposed above the fixedone in each pair on the right side of the weight part 21.

As described above, the left fixed electrodes 31 and the right fixedelectrodes 41 are placed facing the movable electrodes 24, respectively,in the direction parallel to the semiconductor substrate 10. The gapbetween the fixed and movable electrodes of each pair is to detectcapacity, the side surfaces of the electrodes facing each other beingdetecting surfaces.

The left fixed electrodes 31 and the right fixed electrodes 41 areelectrically independent of each other. The fixed electrodes 31 and 41are beams, which have a rectangular cross section and extend parallel tothe movable electrodes 24.

The wiring parts 32 and 42 are supported on the first silicon plate 11through the medium of the oxide film 13, and the left fixed electrodes31 and the right fixed electrodes 41 are cantilevered by the wiring part32 and the wiring part 42, respectively. And the left and right fixedelectrodes 31 and 41 are separated from the oxide film 13.

Thus, a plurality of left fixed electrodes 31 are connected to a singlewiring part 32 and a plurality of right fixed electrodes 41 areconnected to a single wiring part 42.

A pad 30 a for the left fixed electrodes 31 is provided at a prescribedplace on the wiring part 32 and a pad 40 a for the right fixedelectrodes 41 is provided at a prescribed place on the wiring part 42.

A wiring part 25 for the movable electrodes 24 is formed and connectedto the anchor part 23 b as one body, and a pad 25 a for the movableelectrodes 24 is provided at a prescribed place on the wiring part 25.The pads 25 a, 30 a, and 40 a are formed by sputtering or depositingaluminum.

Each of the pads 25 a, 30 a, and 40 a is electrically connected to anexternal circuit (not shown) through a bonding wire. The externalcircuit includes a detecting circuit (see FIG. 5) for processing thesignals outputted from the acceleration sensor 100.

In the acceleration sensor 100 of the present embodiment, a plurality ofthrough holes 26 are made in the relatively large weight part 21 of thesecond silicon plate 12 as a semiconductor layer.

In the present embodiment, as shown in FIG. 3, there are junctions 28 oftwo or three straight parts of the hole frame 27 around the throughholes 26. Namely, there are no junctions of four straight parts or more.

The through holes 26 have a rectangular cross section and are arrangedin zigzag. More specifically, the through holes 26 are arranged in aplurality of rows in the longitudinal direction of the weight part 21(“X” direction), their long sides lying in the same direction, and thethrough holes 26 in the adjacent rows are disposed in zigzag.

Next, the process of making the acceleration sensor 100 willspecifically be described by referring to FIGS. 4A to 4C. FIGS. 4A to 4Care process drawings to show the process of making the dynamic-quantitysemiconductor sensor 100 of the present embodiment.

As shown in FIG. 15A, a mask, whose shape corresponds to the above beamstructure 20-40, is formed of the second silicon plate 12 of the SOIsubstrate 10 by using the photolithography technology.

Thereafter, as shown in FIG. 4B, the second silicon plate 12 isdry-etched with a gas such as CF₄ or SF₆ to form through trenches 14 andthrough holes 26. Thus, the pattern of the above beam structure 20-40 iscollectively formed.

Next, as shown in FIG. 4C, the lower part of the second silicon plate 12is removed by side etching to form the thin part 15. Thus, the movablepart 20 is released. In this way, the acceleration sensor 100 is made.

Because the above side, or release, etching in the weight part 21 ismade through a plurality of through holes 26, the etching is madeefficiently in the acceleration sensor 100 as a semiconductor device ofa surface-processing type. Besides, the through holes 26 reduce theweight of the movable part 20.

Next, the working of the acceleration sensor 100 will be describedbelow. The acceleration sensor 100 detects the applied accelerationbased on the change of capacity between the movable electrodes 24 andthe fixed electrodes 31 and 41 due to the application of acceleration.

As described above, the detecting surfaces of the movable electrodes 24and those of the fixed electrodes 31 and 41 face each other and the gapsbetween the detecting surfaces of the movable electrodes 24 and those ofthe fixed electrodes 31 and 42 are to detect capacity.

A first capacity CS1 is formed between the movable electrodes 24 and theleft fixed electrodes 31; a second capacity CS2, between the movableelectrodes 24 and the right fixed electrodes 41.

When the acceleration sensor 100 is exposed to acceleration containing acomponent which is parallel to the semiconductor substrate 10 and in an“X” direction shown in FIG. 1, the weight part 21 moves in the “X”direction to cause the capacities CS1 and CS2 to change.

For example, when the weight part 21 moves downward in FIG. 1, the gapsbetween the movable electrodes 24 and the left fixed electrodes 31 widenand the gaps between the movable electrodes 24 and the right fixedelectrodes 41 narrow.

Accordingly, the acceleration in the “X” direction is detected based onthe change of the differential capacity (CS1−CS2).

To be specific, a signal based on the capacity difference (CS1−CS2) isoutputted from the acceleration sensor 100, processed in the aboveexternal circuit and the like, and outputted finally.

FIG. 5 shows a detector circuit 200 to detect acceleration at theacceleration sensor 100.

The reference numeral 210 is a switched capacitor circuit (SC circuit),which has a capacitor 211 of capacity “Cf”, a switch 212, and adifferential amplifier circuit 213 and converts the inputted capacitydifference (CS1−CS2) into voltage.

On the other hand, a carrier wave CW1 and another carrier wave CW2 areinputted into the pad 30 a and the pad 40 a, respectively, of theacceleration sensor 100. The amplitude of the carrier waves CW1 and CW2is Vcc and the phase difference between them is 180°. Then, the switch212 of the SC circuit 210 is opened and closed at a prescribed time.

Then, a voltage value V0 representing the applied acceleration in the“X” direction is calculated through the following expression F1 andoutputted.V0=(CS1−CS2)×Vcc/Cf  (F1)

In this way, acceleration is detected.

According to the above embodiment, the trenches 14 are formed in thesecond silicon plate 12 as a semiconductor layer, which is supported onthe first silicon plate 11 as a supporting base plate, by etching. Thetrenches 14 define the movable part 20 which is released from the firstsilicon plate 11. A plurality of through holes 26 is made in the movablepart 20 of the second silicon plate 12. And acceleration, which theacceleration sensor 100 is exposed to, is detected based on thedisplacement of the weight part 21 of the movable part 20. Theacceleration sensor 100 is characterized by junctions 28 of two or threestraight parts of the hole frame 27 around the through holes 26.

As described earlier, the junctions 28 of two or three straight parts ofthe hole frame 27 are accomplished by arranging the rectangular throughholes 26 in zigzag.

According to the above embodiment of the present invention, the numberof straight parts joining at each junction 28 is two or three, whereasthe number of straight parts joining at each junction 28 is four inaccordance with the sensor shown in FIG. 11. The distance from theperimeter to the center “K” of each junction 28 in accordance with theabove embodiment of the present invention is shorter than that of eachjunction 28 in accordance with the prior art.

As shown in FIG. 11, the distance L3 from the perimeter to the center“K” of each junction 28 is about 1.4 times (√{square root over (2)}times) the distance L2 from the periphery of each through hole 26 to thecenter of any straight frame part around said through hole 26.

Accordingly, in the case of the sensor shown in FIG. 11, the timenecessary to release each junction 28 is about 1.4 times the timenecessary to release each straight part of the hole frame.

In the case of the above embodiment of the present invention, thejunctions 28 of three straight parts of the hole frame 27 areaccomplished by arranging the through holes 26 in zigzag. Accordingly,as shown in FIG. 3, the distance L1 from the perimeter to the center “K”of each junction 28 is only about 1.25 times the distance L2 from theperiphery of each through hole 26 to the center of any straight framepart around said through hole 26.

The center “K” of the junction 28 means a point the distances from whichto the nearest parts of the through holes around the junction are equal.

The center “K” is a point where side, or release, etching reaches lastof all. When the center “K” is released, the release etching of themovable part 20 is substantially completed.

Thus, in accordance with the above embodiment of the present invention,the time necessary to release the “L1” parts is only about 1.25 timesthe time necessary to release the “L2” parts. Thus, the time necessaryto release the movable part 20 is reduced to 0.89 (i.e., 1.25/1.4=0.89).

As described above, in accordance with the above embodiment of thepresent invention, the etching time necessary to release the junctions28 is shorter as compared with that of the sensor shown in FIG. 11;therefore, the dispersion of release-etching times of movable parts 20can be minimized.

Thus, in accordance with the above embodiment of the present invention,the movable part 20 of the acceleration sensor 100 can be releasedreliably and the dispersion of finished shapes of movable parts 20 canbe minimized.

In the case of the above embodiment of the present invention, trenchetching is made from the top-surface side of the second silicon plate 12of the SOI substrate 10 to form the pattern of the beam structureincluding the movable part 20 and the lower part of the second siliconplate 12 is removed by side etching to release the movable part 20.

The present invention may be applied to an acceleration semiconductorsensor of the surface-processing type. In this case, trench etching ismade from the top-surface side of the second silicon plate 12 of the SOIsubstrate 10 to form the pattern of the beam structure including themovable part 20 and the movable part 20 is released by makingsacrifice-layer etching through the trenches and thereby removing theoxide film 13.

Besides, the present invention may be applied to angular-velocitysensors.

To sum up, the present invention provides a dynamic-quantitysemiconductor sensor wherein (1) trenches are formed in a semiconductorlayer, which is supported on a supporting base plate, by etching, (2)the trenches define a movable part which is released from the supportingbase plate, (3) a plurality of through holes are made in the movablepart of the semiconductor layer, and (4) dynamic quantity, which isapplied to the dynamic-quantity semiconductor sensor, is detected basedon the displacement of the weight part of the movable part. Thedynamic-quantity semiconductor sensor is characterized by junctions oftwo or three straight parts of the hole frame around the through holes,and the design of the other parts than the junctions of thedynamic-quantity semiconductor sensor can appropriately be changed.

(Second Embodiment)

The acceleration sensor 100 of the above embodiment of the presentinvention is characterized mainly by the junctions 28 of two or threestraight parts of the hole frame 27, which are accomplished by arrangingthe rectangular through holes 26 in zigzag as shown in FIGS. 1 and 3.

Junctions 28 of two or three straight parts of the hole frame 27 can beaccomplished by through holes 26 of other shapes shown in FIGS. 6 to 8.

FIG. 6 shows hexagonal through holes 26 in honeycomb-like arrangement.

In FIG. 7, junctions 28 of two or three straight parts of the hole frame27 is accomplished by giving the shape of “L” to the through holes 26.In FIG. 8, junctions 28 of two or three straight parts of the hole frame27 is accomplished by giving the shape of a cross to the through holes26.

The through holes 26 of FIGS. 6 to 8 bring about the same effect as thethrough holes 26 of FIG. 1.

(Third Embodiment)

The inventors have further preliminarily studied about adynamic-quantity sensor. According to the study by the inventors, it waslearned that the following problem took place in the dynamic-quantitysemiconductor sensor having such a movable part.

Namely, it was newly discovered that in the process where trenches aremade in a semiconductor layer supported on a supporting base plate byetching to form the movable part, the etching rate during the release ofthe movable part depended on the trench width (see FIG. 16).

Accordingly, when releasing the movable part, etching could not beproceeded with at the portion, facing the trench, of the movable parthaving a wide trench width, namely, a wide-gap part (for example, 20 μmwide), and the release could not be accomplished.

In view of the above problem, a dynamic-quantity sensor according to asecond embodiment of the present invention is provided.

FIG. 12 is a schematic plan view of an angular-velocity semiconductorsensor 300 as a dynamic-quantity semiconductor sensor according to anembodiment of the present invention. FIG. 13 is a schematic sectionalview along the line XIII—XIII of FIG. 12. FIG. 14 is an enlarged view ofthe part “XIV” of FIG. 12.

This angular-velocity sensor 300 is made by processing a semiconductorsubstrate 301 comprising a silicon plate, etc.

To be specific, by forming trenches 302 in the semiconductor substrate301 with a known semiconductor fabrication technology such as etching,as shown in FIG. 12, a structure comprising a frame-shaped base 310 as afixed portion, movable parts 320 and 330 movably placed inside the frameof the base 310, etc. is defined and formed.

To be more specific, as shown in FIG. 13, the angular-velocity sensor300 is formed, for example, by using an SOI (Silicon-On-Insulator)substrate 1 as a semiconductor substrate 301, which is made by pastingtwo silicon plates 301 a and 301 b together with an oxide film 301 ctherebetween.

Of the two silicon plates 301 a and 301 b of this SOI substrate 301, afirst silicon plate 301 a (the lower plate in FIG. 13) is used as asupporting base plate. Further, to a second silicon plate 301 b (theupper plate in FIG. 13) as a semiconductor layer, known micro-machiningsuch as trench etching and side etching is given from the top-surfaceside of the second silicon plate 301 b.

With such processing, the above trenches 302 are formed in the secondsilicon plate 301 b. Further, the structures such as the above parts310, 320 and 330 defined by the trenches 302 are formed on the secondsilicon plate 301 b.

In this regard, FIG. 12 shows the top-surface side of the second siliconplate 301 b on which the above structures are formed, namely, thetop-surface side of the semiconductor layer 301 b supported on thesupporting base plate 301 a. Also, as shown by broken lines in FIG. 12and FIG. 13, the portion of the second silicon plate 301 b at the innerside of the base 310 is a thin part 303 which is so made as to allow agap between itself and the oxide film 301 c.

Accordingly, at the inner-side portion of the base 310, namely, at thethin part 303, the second silicon plate 301 b on which the abovestructures are formed is released from the first silicon plate 301 a,namely, the supporting base plate 301 a.

Thus, according to the present example, the second silicon plate 301 bis supported and fixed on the first silicon plate 301 a through themedium of the oxide film 301 c at the base 310, and the movable part 320is movable being released from the first silicon plate 301 a, namely,the supporting base plate 301 a.

As shown in FIG. 12, the movable parts 320 and 330 comprise a generallyrectangular vibration part for drive 320, a vibration part for detection330 in the shape of a rectangular frame surrounding the vibration partfor drive 320, a plurality of (in FIG. 12, four) beam parts for drive321 joining the vibration part for drive 320 with the vibration part fordetection 330, and a plurality of (in FIG. 12, two) beam parts fordetection 331 joining the vibrating part for detection 330 with the base310 surrounding it.

The vibration part for drive 320 is formed as one body with thevibration part for detection 330 through the medium of the beam part fordrive 321. To be more specific, though the vibration part for drive 320is associated with the vibration part for detection 330 and the beampart for detection 331, it is connected with the vibration part fordetection 330, the base 310, and the first silicon plate 301 a as asupporting base plate through the medium of the beam part for drive 321.

Each beam part for drive 321 is folded back in the shape of a U. One endof it is connected to the vibration part for drive 320 and the other endis connected to the inside surface of the vibration part for detection330.

Further, a pair of parallel-bar portions 322 and 323 of the aboveU-shaped beam part for drive 321 are made so as to bend in the directionperpendicular to their longitudinal direction. Therefore, the vibrationpart for drive 320 can vibrate in the “X” direction shown in FIG. 12.The “X” direction will hereinafter be called “first direction X” inwhich the vibration part for drive 320 vibrates.

On the other hand, at each of the beam parts for detection 331, a pairof beams 332 and 333 are placed in parallel so that there is a gaptherebetween, and both the ends of the beams 332 and 333 are joined toform a rectangular frame.

Then, a middle portion of the beam 332 is connected to protrusionsprotruding from the inside surface of the base 310 and fixedly supportedon the base 310. A middle portion of the other beam 333 is connected tothe vibration part for detection 330.

In other words, the vibration part for detection 330 is connected to thebase 310 and the first silicon plate 301 a as a supporting base platethrough the medium of the beam part for detection 331.

Further, at the beam part for detection 331, the pair of parallel beams332 and 333 described above bend in the direction perpendicular to theirlongitudinal direction.

Therefore, the vibration part for detection 330 can vibrate within theplane of the above base 301 in the direction perpendicular to the firstdirection X, which is the direction in which the vibration part fordrive 320 vibrates, namely, in the “Y” direction shown in FIG. 12. The“Y” direction will hereafter be called “second direction Y” in which thevibration part for detection 330 vibrates.

Further, on the outer circumference of the vibration part for detection330, protrusions 335 in the shape of a comb's teeth protruding towardthe internal circumference of the base 310 facing the outercircumference are formed. Also, another protrusions 311 in the shape ofa comb's teeth are formed on the internal circumference of the base 310.The protrusions 335 and the protrusions 311 are arranged alternately andmakeup electrode parts for detection 311 and 335 of the sensor 300.

The electrode parts for detection 311, 335 and the movable parts 320,330 are both joined to the base 310. However, since trenches (not shown)are formed in the base 310, the electrode parts for detection 311, 335and the movable parts 320, 330 are electrically independent of eachother.

Thus, in the angular-velocity sensor 300, through trenches 302 areformed in the second silicon plate 301 b by etching the second siliconplate 301 b as a semiconductor layer supported on the first siliconplate 301 a as a supporting base plate.

The movable parts 320 and 330 released from the first silicon plate 301a are provided in the second silicon plate 301 b. The movable parts 320and 330 comprise a vibration part for drive 320 and a vibration part fordetection 330.

The vibration part for detection 330 is joined to the first siliconplate 301 a from the base 310 through the medium of the beam part fordetection 331, which can move in the second direction Y. Also, thevibration part for drive 320 is joined to the vibration part fordetection 330 through the medium of the beam part for drive 321, whichcan move in the first direction X.

With respect to the angular-velocity sensor 300, according to thepresent embodiment, as shown in FIGS. 12 to 14, besides the trenches 302(302 c, 302 d) in the outer region of the movable parts 320 and 330,trenches 302 (302 a, 302 b) are formed in the movable parts 320 and 330,namely, in the vibration part for drive 320 and the vibration part fordetection 330.

Further, in the inner region of the base 310, trenches are not formed inbeams 321 and 331, whose areas are relatively small and not etched, andin the portions in the shape of a comb's teeth 311 and 335. The trenches302 a and 302 b are formed in other portions whose areas are relativelylarge, namely, in the vibration part for drive 320 and the vibrationpart for detection 330.

As described above, the angular-velocity sensor 300 is made by using thefirst silicon plate 301 a of the SOI substrate 301 as a supporting baseplate and by performing trench etching and side etching from thetop-surface side of the second silicon plate 301 b to form movable parts320 and 330, which are released from the first silicon plate 301 a, inthe second silicon plate 301 b.

Therefore, according to the present embodiment, a plurality of trenches302 a and 302 b are formed in the movable parts 320 and 330 where areasare large and not etched to raise the efficiency of etching and toreduce the weight of the angular-velocity sensor 300 as such asemiconductor device of the surface-processing type.

As shown in FIG. 14, according to the present embodiment, of all thetrenches 302 of the sensor 300, the width W1 of the trenches 302 aformed in the movable parts 320 and 330 is set such that the etchingrate during the release becomes fastest.

In particular, according to the present embodiment, as shown in FIG. 14,the trenches 302 c and 302 d provided in the outer region of the movableparts 320 and 330 are the trench 302 c of the portion whose width W3 isrelatively wide and the trench 302 d of the portion whose width W4 isrelatively narrow.

Then, of the trenches 302 a and 302 b formed in the movable parts 320and 330, the width W1 of the trench 302 a formed in the portion facingthe trench 302 c of the portion whose width W3 is relatively wide is setsuch that the etching rate during the release becomes fastest in thesensor 300.

Further, of the trenches 302 a and 302 b formed in the movable parts 320and 330, the width W2 of the trench 302 b formed in the portion facingthe trench 302 d of the portion whose width W4 is relatively narrow isset such that the etching rate is slower than that of the case of thewidth W1 of the trench 302 a formed in the portion facing the trench 302c of the portion whose width W3 is relatively wide.

Further, the width of a trench referred to in the present embodiment isthe width along the direction perpendicular to the longitudinaldirection of the trench, namely, so-called trench line width.

Next, the process of making the angular-velocity sensor 300 willspecifically be described by referring to FIGS. 15A to 15C. FIGS. 15A to15C are process drawings to show the process of making theangular-velocity sensor 300.

As shown in FIG. 15A, a mask, whose shape corresponds to the abovestructure 310–330, is formed of the second silicon plate 301 b of theSOI substrate 301 by using the photolithography technology.

Thereafter, as shown in FIG. 15B, the second silicon plate 301 b isdry-etched with a gas such as CF₄ or SF₆ to form trenches 302. Thus, thepattern of the above structure 310–330 is collectively formed.

Next, as shown in FIG. 15C, the lower part of the second silicon plate 1b is removed by side etching to form the thin part 3. Thus, the movableparts 320 and 330 are released. In this way, the angular-velocity sensor300 is made.

Next, the working of the angular-velocity sensor 300 having such aconfiguration will be described. First, by electromagnetic drive orcapacitive drive etc., the vibration part for drive 320 is vibrated(drive-vibrated) in the first direction X in FIG. 12.

Under this drive vibration, as shown in FIG. 12, when theangular-velocity sensor 300 is exposed to angular velocity Ω appliedaround the axis in the vertical direction in FIG. 12, namely, around theaxis perpendicular to the first direction X and the second direction Y,a Coriolis force is generated in the second direction Y with respect tothe vibration part for drive 320.

This Coriolis force is transmitted from the beam part for drive 321 tothe vibration part for detection 330, and the vibration part fordetection 330 and the vibration part for drive 320 vibrate (detectionvibration) as one body in the second direction Y in FIG. 12. Due to thisdetection vibration, the distance between the above protrusions 311 and335 varies. By detecting the change in the distance as variations incapacity between the protrusions 311 and 335 through the medium of awiring part, etc. (not shown) formed on the base 310, the above angularvelocity Ω is detected.

According to the present embodiment, the through trenches 302 are formedin the second silicon plate 301 b, which is supported on the firstsilicon plate 301 a, by etching. The movable parts 320 and 330 definedby the trenches 302 and released from the first silicon plate 301 a areprovided in the second silicon plate 301 b. And angular velocity Ω,which the angular-velocity sensor 300 is exposed to, is detected basedon the displacement of the movable parts 320 and 330. Of the trenches302, the width W1 of the trenches 302 a formed in the movable parts 320and 330 is set such that the etching rate becomes fastest in the sensor300.

The movable parts 320 and 330 are release-etched from the trenches 302provided in the outer regions of the movable parts 320 and 330. In thepresent embodiment, the width W1 of the trench 302 a formed in themovable parts 320 and 330 is set such that the etching rate during therelease becomes fastest in the sensor 300. Therefore, the etching timefor the movable parts 320 and 330 can be minimized.

Therefore, according to the present embodiment, the movable parts 320and 330 of the angular-velocity sensor 300 can reliably be released byetching.

As described above (see FIG. 14), there are trenches 302 c and 302 dformed in the outer regions of the movable parts 320 and 330 of theangular-velocity sensor 300 according to the present embodiment. One ofthem has a relatively wide width W3 and the other of them has arelatively narrow width W3. Of the trenches 302 a and 302 b formed inthe movable parts 320 and 330, the width W1 of the trench 302 a formedin a portion facing the trench 302 c having the above relatively widewidth W3 is set such that the etching rate becomes fastest in the sensor300.

Of the movable parts 320 and 330, the portion facing the trench 302 chaving the relatively wide width W3 is the one where the etching rate ofthe release is inherently slow. In the present embodiment, however,since the trench 302 a has such a width W1 that the etching rate becomesfastest, appropriate release etching can be performed there, which ispreferable.

Further, as described above (see FIG. 14), with respect to the angularvelocity sensor 300 of the present embodiment, of the trenches 302 a and302 b formed in the movable parts 320 and 330, the width W2 of thetrench 302 b formed in the portion facing the trench 302 d having theabove relatively narrow width W4 is the one whose etching rate is slowerthan that of the width W1 of the trench 302 a formed in the portionfacing the trench 302 c having the above relatively wide width W3.

Of the movable parts 320 and 330, the portion facing the trench 302 dhaving the relatively narrow width W4 is the one where the etching rateduring the release is faster than that of the portion facing the trench302 c having the relatively wide width W3. However, in accordance withthe present embodiment, excessive etching can be prevented at theportions facing the trenches 302 d having the relatively narrow width W4in the movable parts 320 and 330.

Referring also to FIGS. 16 and 17, the above effects of the presentembodiment will be described more specifically.

FIG. 16 shows the result of the research conducted by the inventor etal. with respect to the relation between the trench width (unit: μm) andthe rate of release etching (unit: μm/min). Further, FIG. 17 is a planview showing a comparative example adopting a conventional trenchconfiguration in the angular velocity sensor 300 of the presentembodiment, which is shown from the same observing point as in FIG. 14.

As shown in FIG. 16, the etching rate reaches the maximum value at acertain trench width. In this case, the etching rate reaches the maximumvalue when the trench width is at P1 in FIG. 16, for example, around 7μm. After the trench width exceeding the value of about 10 μm, theetching rate is getting close to zero.

In the case of the present embodiment shown in FIG. 14, the relativelywide width W3 of the trenches 302 c formed in the outer regions of themovable parts 320 and 330 is 10 μm or wider, for example, about 20 μm.

Further, of the trenches 302 a and 302 b formed in the movable parts 320and 330, the width W1 of the trench 302 a formed in the portion facingthe trench 302 c having the above relatively wide width W3 is about 7μm, which allows the fastest etching rate.

Further, of the trenches 302 a and 302 b formed in the movable parts 320and 330, the width W2 of the trench 302 b formed in the portion facingthe trench 302 d having the above relatively narrow width W4 is the onewhere the etching rate is slower than that of the case of the abovewidth W3. For example, it may be 3 μm or 9 μm, which corresponds to P2in FIG. 16. In FIG. 14, the width W2 is about 3 μm.

In this way, according to the present embodiment, in a portion where theetching rate during the release is relatively slow in the movable parts320 and 330, the etching time is shortened to achieve the reliablerelease. Also, in a portion where the etching rate is relatively fast inthe movable parts 320 and 330, excessive etching can be prevented.

On the contrary, in the comparative example in FIG. 17, the widths W2 ofthe trenches 2 b in the movable parts 320 and 330 are all substantiallythe same. Therefore, of the movable parts 320 and 330, at the portionfacing the trench 302 d having a relatively narrow width W4, reliablereleasing is performed. However, of the movable parts 320 and 330, atthe portion facing the trench 302 c having a relatively wide width W3,some areas are not etched, which may result in incomplete releasing.

As described above, according to the present embodiment, in theangular-velocity sensor 300 as a dynamic-quantity semiconductor sensorwhere trenches 302 are made in the semiconductor layer 301 b supportedon the base plate 301 a by etching to form movable parts 320 and 330,which are released from the base plate 301 a, the movable parts 320 and330 can reliably be released by etching.

According to the above embodiment, the trenches 302 a having such awidth W1 that allows the etching rate to be fastest in the sensor 300are formed in the movable parts 320 and 330. However, they may be thetrenches formed in the outer regions of the movable parts 320 and 330,namely, in FIG. 14, the trenches 302 c and 302 d that define the outsideshapes of the movable parts 320 and 330.

Besides, the present invention may be applied to acceleration sensors.

To sum up, the present invention provides a dynamic-quantitysemiconductor sensor wherein (1) through trenches are formed in asemiconductor layer, which is supported on a supporting base plate, byetching, (2) the trenches define a movable part which is released fromthe supporting base plate, and (3) dynamic quantity, which is applied tothe dynamic-quantity semiconductor sensor, is detected based on thedisplacement of the movable part. The dynamic-quantity semiconductorsensor is characterized in that the widths of the trenches formed in themovable parts or in the outer regions of the movable parts are set suchthat the etching rate becomes fastest in the sensor. The design of otherparts of the dynamic-quantity semiconductor sensor can appropriately bechanged.

Such changes and modifications are to be understood as being within thescope of the present invention as defined by the appended claims.

1. A semiconductor physical quantity sensor comprising: a substrate; asemiconductor layer supported on the substrate; a trench disposed in thesemiconductor layer; and a movable portion disposed in the semiconductorlayer and separated from the substrate by the trench, wherein themovable portion includes a plurality of through-holes, each of whichpenetrates the semiconductor layer in a thickness direction, the movableportion is capable of displacing on the basis of a physical quantityapplied to the movable portion so that the physical quantity is detectedby a displacement of the movable portion, the movable portion includes acenter portion and a periphery portion, the movable portion has aplurality of junctions disposed among the through-holes, each of theplurality of junctions has a trifurcate shape at least in the centerportion, the movable portion provides a through-hole frame including aplurality of rods, each of the plurality of junctions being formed by anintersection of a number of the plurality of rods, each of the pluralityof rods having a width in a horizontal direction perpendicular to athickness direction, and a distance between a center of each of theplurality of junctions and a corner of a neighboring trench is smallerthan (√{square root over (2)}/2) tunes the width of each of theplurality of rods.
 2. The sensor according to claim 1, wherein eachthrough-hole has a rectangular shape, and the through-holes are arrangedto be houndstooth check structure.
 3. The sensor according to claim 1,wherein each through-hole has a hexagonal shape, and the through-holesare arranged to be honeycomb structure.
 4. The sensor according to claim1, wherein each of the plurality of rods is uniform in width.
 5. Asemiconductor physical quantity sensor comprising: a substrate; asemiconductor layer supported on the substrate; a trench disposed in thesemiconductor layer; and a movable portion disposed in the semiconductorlayer and separated from the substrate by the trench, the movableportion including a plurality of through-holes, each of which penetratesthe semiconductor layer in a thickness direction, the movable portioncapable of being displaced based on an applied physical quantity so thatthe applied physical quantity is detected by a displacement of themovable portion, the movable portion including a plurality of junctionsthat are disposed among the plurality of through-holes and that areformed by an intersection of a number of a plurality of straight partsof the movable portion, wherein a distance between a center of each ofthe plurality of junctions and respective corners of neighboringtrenches is smaller than (√{square root over (2)}/2) times a width ofeach of the plurality of straight parts of the movable portion.